let in vs observe

let in

verb
  • To divulge one's inner thoughts to (someone), making oneself emotionally vulnerable to them; to open up to (someone). 

  • To associate with. 

  • To let someone or something come in; to admit someone or something in. 

observe

verb
  • To comment on something; to make an observation. 

  • To take note of and celebrate (a holiday or similar occurrence); to follow (a type of time or calendar reckoning). 

  • To notice or view, especially carefully or with attention to detail. 

  • To follow or obey the custom, practice, or rules (especially of a religion). 

How often have the words let in and observe occurred in a corpus of books? (source: Google Ngram Viewer )